1. Field of the Invention
The present invention relates to a rotary diamond tool suitable for truing a grinding wheel made of hard abrasive grains such as cubic boron nitride, diamond or the like.
2. Discussion of the Prior Art
In the past, a single-point type diamond tool 7 shown in FIG. 7 was widely used for truing a grinding wheel. The diamond truing tool was composed of a base 71 made of steel and a single diamond 72 which is partially buried in the front end of the base 71.
The single-point type diamond tool 7 is capable of truing a grinding surface of a grinding wheel with an appropriate surface roughness, thereby reducing the grinding resistance of the grinding wheel. The diamond tool 7, however, has a disadvantage that the life time thereof is relatively short, because the top tip of the diamond 72 wears rapidly and it is difficult to keep the sharpness of the diamond 72. Therefore, the diamond tool 7 cannot be used in an automated truing apparatus in which the diamond truing tool is required to have a long life. Further, the diamond tool 7 has another disadvantage that the truing ability is instable, because it has an anisotropic of hardness due to the crystal orientation. Namely, the hardness of the diamond changes depending upon the direction of force applied to the diamond.
Also, a diamond truing tool 8 shown in FIG. 8 has been used for truing a grinding wheel. The diamond truing tool 8 is a metal-bonded grinding wheel containing a lot of diamond abrasive grains 81 which are united each other with binding agent 82 such as nickel by a powder metallurgy process. The diamond truing tool 8 is formed in a thin cylindrical shape, and held by a pair of mounting flanges 21 through which the diamond truing tool 8 is attached to the rotary spindle of a truing device (not shown) using a nut.
Although the diamond truing tool 8 has an advantage of long life, the diamond truing tool 8 has a disadvantage that it is difficult to form sharp cutting edges on the periphery surface thereof, and therefore difficult to reduce the grinding resistance of a grinding wheel to a sufficient level by a truing operation. Also, the diamond truing tool 8 has another disadvantage that the stiffness thereof is not sufficient, because the thickness thereof is small. Therefore, the periphery cutting portion of the tool 8 tends to vibrate, resulting in positional changes of the cutting portion during truing operations. Further, when the diamond truing tool 8 is used, the amount of cut-in feed during the truing operation is limited within a predetermined range corresponding to the stiffness of the tool 8. Therefore, the truing efficiency cannot be increased so much.